with data as (select level levels from dual
 connect by level <= &how_may_rows) 
select f from data 
 model dimension by (levels) 
 measures ( 0 f) 
 rules ( f[1] = 0 , f[2] = 1 , f[levels>2]=f[cv(levels)-2]+f[cv(levels)-1]
);
Enter value for how_may_rows: 10

Details in http://arjudba.blogspot.com/2008/10/how-to-generate-fibonacci-series-in.html